JPS6155547B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a recording liquid using finely dispersed pigment as a colorant, and particularly relates to a method for producing a recording liquid suitable for an inkjet recording method. 2. Description of the Related Art Conventionally, inks used in writing instruments such as felt pens and fountain pens have been known to have various dyes and pigments dissolved or dispersed in a liquid medium consisting of water or other organic solvents. Furthermore, the above-mentioned composition is also used in the so-called inkjet recording method, in which recording is performed by ejecting the liquid in the recording head from the ejection orifice using vibration by a piezo vibrator, electrostatic attraction by applying high voltage, thermal energy, etc. known to be used. Writing instruments such as felt pens and fountain pens have many properties in common with inkjet recording liquids, such as the absence of clogging due to ink drying at the tip and good water resistance and light resistance of recorded images. However, compared to writing instruments (stationery), recording liquid for inkjet has low ejection responsiveness and ejection stability when droplets are generated from minute orifices (a wide stable ejection margin against fluctuations in drive voltage and drive frequency), and ejection similar to printers. When recording while a recording head with an orifice moves left and right, the ejection orifice must hold the recording liquid well against inertial force, and it must penetrate quickly into the recording material such as paper to prevent blurring. Even stricter conditions are required, such as the absence of The inkjet recording method uses a method of generating droplets and a method of controlling the flight direction of the droplets.
There are various methods. An example is shown in FIG. That is, the apparatus shown in FIG. 1 applies a recording signal to a recording head section having a piezo vibrator, and performs recording by generating droplets of recording liquid in response to the signal.
In FIG. 1, reference numeral 1 denotes a recording head, which has a piezo vibrator 2a, a diaphragm 2b, an inlet 3 for recording liquid, a liquid chamber 4 in the head, and an ejection port (ejection orifice) 5. A recording liquid 7 stored in a storage tank 6 is introduced into the liquid chamber 4 through a supply pipe 8 . Incidentally, an intermediate treatment means 9 such as a pump or a filter may be provided in the middle of the supply pipe 8 depending on the case. And in the piezo vibrator 2a,
A signal converted from the recording signal S into a pulse by the signal processing means (for example, a pulse converter) 10 is applied, and a pressure change occurs in the recording liquid in the liquid chamber 4 in accordance with the signal. As a result, the recording liquid 7 is ejected from the ejection orifice 5 as a droplet 11, and the recording member 12
Recording is done on the surface of the In addition to the above devices, various types of devices are known. For example, as shown in FIG.
As a modification of the figure, there is a device in which the liquid chamber 4 is shaped like a knob and a cylindrical piezo vibrator is installed around the outer periphery (the mechanism of droplet generation in this device is essentially the same as in FIG. 1). (same as the equipment shown). Also, a device that continuously generates charged droplets and uses a portion of the droplets for recording. Alternatively, there is also known an apparatus that applies thermal energy corresponding to a recording signal to the recording liquid in the chamber of a recording head and generates droplets using the energy. An example thereof is shown in Fig. 3-a, Fig. 3-b, and Fig. 4. The head 13 is made of glass, ceramic, plastic plate, etc., having grooves 14 through which ink passes, and a heat-generating head 15 used for thermal recording (a thin film head is shown in the figure, but is not limited to this). Obtained by gluing. Heat generating head 15
consists of a protective film 16 made of silicon oxide or the like, aluminum electrodes 17-1, 17-2, a heating resistor layer 18 made of nichrome or the like, a heat storage layer 19, and a substrate 20 with good heat dissipation properties such as alumina. There is. The ink 21 has reached the discharge orifice 22 and forms a meniscus 23 due to the pressure P. Now, when an electric signal is applied to the electrodes 17-1 and 17-2, the part of the heating head 15 indicated by n suddenly generates heat, bubbles are generated in the ink 21 in contact with this part, and the pressure causes the meniscus 23 to is destroyed and the ink 21 is ejected from the ejection orifice 22 into a recording droplet 2.
4 and flies toward the recording member 25. FIG. 4 shows an external view of a multi-head in which a large number of heads shown in FIG. 3-a are arranged. The multi-head is made by gluing together a glass plate 27 having multi-grooves 26 and a heating head 28 similar to that described in FIG. 3-a. Conventionally, recording liquids for stationery or inkjet have been used, for example, in JP-A-50-91427 and JP-A-51-
90624, Japanese Patent Publication No. 51-40484, Japanese Patent Publication No. 52-13126, Japanese Patent Publication No. 52-13127, and Japanese Patent Publication No. 50-95008, various dye pigments are dissolved or dispersed in aqueous or non-aqueous solvents. ing. Common desirable conditions for recording liquids for stationery and inkjet are: (1) No clogging due to drying at the tip of the pen or orifice, and (2) Good for recording materials (paper, cloth, film, etc.). (3) The recorded image has a clear color tone and high density; (4) The recorded image has excellent water resistance and light resistance; (5) The surrounding materials of the recording liquid ( (6) It must have excellent safety characteristics such as odor, toxicity, and flammability. In addition, the recording liquid for inkjet has liquid physical properties (viscosity, surface tension conductivity, etc.) that match the ejection conditions (driving voltage, driving frequency, ejection orifice shape and material, orifice diameter, etc.) and can last for a long time. It is required that the discharge stability is as high as possible. It is quite difficult to satisfy the above characteristics at the same time, and the previously known techniques described above were unsatisfactory in this respect. Dyes and pigments used in this type of recording liquid include, for example, Japanese Patent Publication No. 52-13126, Japanese Patent Application Publication No. 49-89534, Japanese Patent Application Publication No. 50-95008, and Japanese Patent Application Publication No. 53-1989.
77706, disclosed in Japanese Patent Application Laid-Open No. 51-90624. However, dyes such as direct dyes, acid dyes, and basic dyes generally have problems in the water resistance and light resistance of recorded images, and pigments have problems in that they have poor dispersion stability and are prone to clogging. The present invention eliminates the drawbacks of the conventional example described above and satisfies ejection stability, long-term storage stability, fixing performance, image density, clarity, water resistance, light resistance, and also odor, toxicity, flammability, etc. The present invention aims to provide a suitable manufacturing method for obtaining a highly practical recording liquid with excellent safety. The production method of the present invention is characterized in that, in producing a recording liquid containing at least a pigment, a dispersant, and a liquid medium, the pigment is synthesized in the liquid medium in which the dispersant is present. That is, the present invention relates to a method for producing a highly practical recording liquid that can be produced by a simple method and that takes advantage of the excellent water resistance and light resistance of pigments to improve the dispersion stability that was a drawback of pigments. Furthermore, a feature of the present invention is that the pigment is synthesized in a liquid medium containing a dispersant and used as a recording liquid either as it is or by simply removing impurities such as inorganic salts by ultrafiltration or reverse osmosis. . Therefore, compared to conventional techniques in which a recording liquid is produced by mixing and grinding a pigment, a dispersant, and a liquid medium using a dispersion device such as a ball mill, sand mill, or roll mill, the pigment can be dispersed in a much finer and more stable manner. can be obtained. The pore diameter of the ink ejection opening of stationery and inkjet recording heads is several tens to several hundred microns. In conventional production methods in which pigments are dispersed together with a dispersant and a liquid medium using a dispersion machine such as a ball mill, the particle size of the pigment obtained is at most on the order of several hundred millimicrons, and often ranges from several microns to several tens of microns.
The presence of micron-sized coarse particles blocks the ink ejection port, causing clogging. Further, even if coarse particles are removed by centrifugation or filtration after production, the dispersion state is not stable to begin with, and if left for a long time, the particles will re-agglomerate, become coarse particles, and settle. According to the production method of the present invention, the pigment particle size is 1 to
It is in the range of 100 millimicrons and will not re-agglomerate even after long-term storage. In order to further enhance stability during long-term storage, it is desirable to remove unreacted intermediates and inorganic salts produced during pigment synthesis by a commonly used ultrafiltration method. Pigments used in the present invention include, for example, inorganic pigments such as iron black, navy blue, Bengara, and ultramarine, and azo pigments,
Examples include organic pigments such as phthalocyanine, quinacridone, indigo, dioxazine, perinone-perylene, isoindolinone, and phthalone. In the method for producing a recording liquid of the present invention, the preferred content of pigment in the recording liquid is 1 to 30% by weight. Dispersants used in the present invention include known anionic, nonionic, cationic, and amphoteric surfactants, but particularly preferred dispersants include polymeric dispersants with a molecular weight of 500 to 100,000. It will be done. One example of a preferred polymer dispersant is:
Polyvinyl alcohol, polyvinylpyrrolidone, polyvinylpyridine, polyacrylate, polymethacrylate, all having the above molecular weight range,
Condensed naphthalene sulfonate, olefin-maleic anhydride copolymer (olefin includes ethylene, styrene, isobutylene, diisobutylene, α-olefin, vinyl ether, etc.) and its derivatives (maleate or amide, etc.), polyoxyethylene , polyoxypropylene, polyoxyethylene-polyoxypropylene block polymer, styrene-(meth)acrylic acid (salt) copolymer, (meth)acrylic acid ester-(meth)acrylic acid (salt) copolymer, styrene- Itaconic acid (salt) copolymer, itaconic acid ester-itaconic acid (salt) copolymer, vinylnaphthalene-maleic anhydride (salt) copolymer, vinylnaphthalene-(meth)acrylic acid copolymer, vinylnaphthalene- Itaconic acid (salt) copolymer, etc. In addition, polymeric dispersants in which monomers such as acrylonitrile, vinyl acetate, (meth)acrylamide, N-methylol (meth)acrylamide, vinyl chloride, vinylidene chloride, etc. are further copolymerized with the above polymers are also preferably used. can. These polymeric dispersants are synthesized by known polymerization methods such as radical polymerization. The amount of the dispersant used in the present invention is preferably 1 to 500 weight percent, more preferably 5 to 300 weight percent, based on the pigment content. The liquid medium of the present invention is water or water consisting of an aqueous solvent obtained by mixing water and a water-miscible organic solvent and a known organic solvent such as hydrocarbons, ketones, esters, alcohols, ethers, and amides. Both solvent-free solvents can be used. However, preferably an aqueous liquid medium of water and water-miscible organic solvents is used. Examples of water-miscible organic solvents that are preferably used include methyl alcohol, ethyl alcohol, propyl alcohol, diacetone alcohol, furfuryl alcohol, ethylene glycol, propylene glycol, butylene glycol, diethylene glycol, dipropylene glycol, and triethylene. Glycol, glycerin, tetraethylene glycol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, methyl carbitol, ethyl carbitol, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, methyl carbitol acetate, ethyl carbitol acetate, These include diacetone alcohol, diethanolamine, triethanolamine, formamide, acetamide, dimethylacetamide, and the like. The preferred content of these water-miscible organic solvents is 5 to 80 weight percent in the liquid medium, more preferably 10 to 50 weight percent. In addition, conventionally known viscosity modifiers, surface tension modifiers, conductivity modifiers, binders, etc. can be added to the recording liquid produced in the present invention. The invention will be explained in more detail in the following examples.
In addition, the number of parts in the examples is the number of parts by weight. Example 1 A base pickling solution was prepared according to the following composition in a beaker equipped with a stirrer and cooled to 5°C. In a separate beaker, diazotization was carried out using the following composition in a conventional manner to prepare a diazo solution. The diazo solution was added dropwise to the presoaking solution over about 30 minutes while stirring to perform coupling. After dropping, lower the liquid temperature to 10
After raising the temperature to ℃ and reacting for another 2 hours, add 30% acetic acid water.
It was neutralized by adding 1. The resulting blue pigment dispersion is subjected to ultrafiltration using a polyolefin ultrafiltration membrane with a molecular weight fraction of 6000, and ion-exchanged water is added to the amount of the liquid to remove low-molecular impurities such as salts. A stably dispersed recording liquid was obtained.

【table】

[Table] A recording device having an on-demand recording head (discharge orifice diameter 50μ, piezoelectric vibrator drive voltage 60V, frequency 4KHz) that ejects the recording liquid using a piezoelectric vibrator uses the recording liquid at T ₁ to T. ₄ studies were conducted, and good results were obtained in all cases. (T ₁ ) Long-term storage stability of the recording liquid: Even after the recording liquid was sealed in a glass container and stored at -30℃ and 60℃ for 6 months, no precipitation of insoluble matter was observed, and the physical properties and color tone of the liquid did not change. I was bored. (T ₂ ) Ejection stability: Continuous ejection was performed for 24 hours in an atmosphere of room temperature, 5° C., and 40° C. Under all conditions, stable high-quality recording was possible from beginning to end. (T ₃ ) Ejection response: Intermittent ejection every 2 seconds and ejection after being left for 2 months were investigated, and in both cases stable and uniform recording was achieved without clogging at the orifice tip. (T ₄ ) Quality of recorded images: The recorded images had high density and were clear. After 6 months of exposure to room light, the density reduction rate was less than 1%, and when immersed in water for 1 minute, no image bleeding was observed. Example 2 In the same manner as in Example 1, a pigment was synthesized by coupling a submerging liquid and a diazo liquid with the composition shown in Table 1, and then subjected to ultrafiltration to remove impurities, and then subjected to centrifugation. Coarse particles were further removed to obtain a recording liquid. Similar tests were conducted using the same equipment as in Example 1, and excellent results were obtained in all cases. As a reference example, a pigment slurry obtained by removing the dispersant added to the base pickling liquid and performing coupling was washed with water and dried to produce a pigment powder.The dispersant and liquid medium were added again to the pigment powder, and the mixture was milled in a ball mill. A test similar to that in Example 1 was conducted using a recording liquid prepared by dispersion for 24 hours. As a result, in the test (T ₁ ), precipitates were formed in all cases, and in the test (T ₂ ), clogging occurred during the continuous discharge test for 1 to 3 hours, resulting in failure to discharge.

[Table] Example 3 Using the recording liquid of Example 1, an on-demand type multi-head (discharge orifice diameter 35μ, heating resistor Body resistance value 150
Ω, driving voltage 30V, frequency 2KHz)
The same study as in Example 1 was conducted using the recording device shown in the figure, and excellent results were obtained. Example 4 In a four-necked flask equipped with a stirrer, 250 parts of trichlorobenzene, 37 parts of phthalic anhydride, 60 parts of urea, 7 parts of cuprous chloride, 1 part of arsenic oxide, and Unilube 40DP-
Add 100 parts of 50B (ethylene oxide-propylene oxide block polymer: NOF Corporation).
After heating to 160°C and reacting for 1 hour, the temperature was raised to 200°C and kept for 5 hours. When the obtained recording liquid in which copper phthalocyanine was dispersed was subjected to the same test using the same apparatus as in Example 1, excellent results were obtained in all cases. Example 5 Each of the recording liquids obtained in Example 2 was individually filled into a felt pen, the cap was removed, and the liquid was left for one week before writing.
The recorded images had extremely excellent water resistance and light resistance. As explained above, by using the recording liquid produced according to the present invention, (1) the liquid has good long-term storage stability and is less likely to clog the pen tip or orifice; (2) Wide allowance for stable discharge against fluctuations in temperature and driving conditions. (3) Fixation on the recording member is fast and the image is clear. (4) The printed matter has good water resistance and light resistance. (5) The recording liquid is highly safe and does not attack surrounding materials (containers, sealing materials). There are advantages such as

[Brief explanation of the drawing]

1 and 2 are schematic diagrams of an inkjet recording apparatus, respectively. Figures 3-a and 3-b are a vertical sectional view and a horizontal sectional view of a main part of another recording device. FIG. 4 is an external perspective view of a multi-head head shown in FIGS. 3-a and 3-b. However, in the figure, 1...recording head, 2a...
...Piezo vibrator, 2b...Vibration plate, 3...Inflow port, 4...Liquid chamber, 5...Discharge orifice, 6...
Storage tank, 7... Recording liquid, 8... Supply pipe, 9...
...Intermediate processing means, 10...Signal processing means, 11...
...Droplet, 12, 25... Recording material, S... Recording signal, 14... Liquid chamber, 15... Heat generating head, 16...
... protective layer, 17 ... electrode, 18 ... heat generating resistor layer, 19 ... heat storage layer, 20 ... substrate, 26 ... groove.

Claims (1)

[Claims] 1. A method for producing a recording liquid, characterized in that, in producing a recording liquid containing at least a pigment, a dispersant, and a liquid medium, the pigment is synthesized in a liquid medium in which the dispersant is present. . 2. The method for producing a recording liquid according to claim 1, wherein the pigment is synthesized in a liquid medium containing a dispersant and then purified by ultrafiltration or reverse osmosis. 3. The method for producing a recording liquid according to claim 1, wherein the pigment has a particle size in the range of 1 to 100 millimicrons. 4. The method for producing a recording liquid according to claim 1, wherein the dispersant is a polymer having a molecular weight in the range of 500 to 100,000. 5. The method for producing a recording liquid according to claim 1, wherein the liquid medium is an aqueous medium containing a nonvolatile organic solvent.